Dawn of the Tiberium Age (DTA) is a stand-alone mod that combines Tiberian Dawn (C&C 95) and Red Alert. While classic mode gets as close to the original game-play and balance as possible, Enhanced mode provides improved game balance and a lot of fun new stuff.
DTA features many customization options for Skirmish and multiplayer (where you can play as GDI, Nod, Allies and Soviet on over 100 maps), challenging original singleplayer missions, as well as co-op missions.
Since this is a stand-alone mod, you don't require anything but the mod itself to be able to play: the original game is not required.